See Figures 1 and 2
The rear wheels on all BMW vehicles, and the front wheels on the 325ix are connected to the differentials by way of constant velocity joints. These swivel joints allow the wheels to rotate freely, while being able to move up and down independently of the opposite wheel.
The constant velocity joint is surrounded by a heavy moly-type grease which helps keep the parts cool, reducing wear, while enabling the components to move with ease. These joints are covered by rubber boots which need to be inspected regularly. In the event a boot tears, the grease inside will escape, allowing dirt any other foreign matter to enter, quickly destroying the entire joint.
To inspect a CV-boot, raise the vehicle and support it safely on jackstands. Using a light, inspect each boot for cracks or tears or missing retinning clamps. There should be no visible signs of grease on the exterior of the boot or the surrounding components, and the boot should feel firm when grasp, revealing that the joint has enough grease.
In the event the boot and/or CV-joint need replacing or other type of service, refer to the procedures in Steering & Suspension of this repair guide.